Techniques of heating an object for soldering using concentrated infra-red energy are disclosed in the prior art, as exemplified by U.S. Pat. Nos. 3,592,992 and 3,710,069. In these known systems, a source of infra-red light is placed at a first focal point within an elliptical reflector, and the light emitted from the source is reflected to a second focal point and utilized to heat or otherwise work on an object.
In many applications, it is desired that the reflected infra-red energy be focused at a point. This cannot be completely achieved unless the infra-red light source is a point source, which is essentially impossible in view of available infra-red sources. Therefore, it is desired to have the workpiece to be acted upon at, or essentially at, the second focal point to minimize the area of heating and to concentrate the reflected energy in this area. If the workpiece is axially spaced to either side of the second focal point, the area which is heated will be greater, and the reflected energy less per unit area. However, with the workpiece precisely positioned in the plane of the second focal point, the workpiece may be subjected to maximum heat in a small controlled area for a limited period of time so that heat transfer to adjacent area is minimized.
In some applications, the control of heat on the workpiece to be soldered or heated can be quite critical. For example, in the fabrication of dental bridges with crowns, the time of application of high heat can be quite critical. The present practice of soldering crowns together to form a bridge involves the use of gas torches which produce a flame of 4400.degree.-5000.degree. F. depending upon the type of gas being combusted. The crowns are generally cast from alloys which have a melting point of less than 2200.degree. F. Thus, to melt a flux on the surfaces of the crowns to be soldered, and then to liquify a solder perform between the crowns to produce bonding thereof, is a very precise operation which requires much skill in conducting the point of application of heat and the time the source heat is applied.
The present invention overcomes these problems by providing a new and improved apparatus and method for localizing heat and controlling the temperature and time of application of the heat energy so as not to damage a workpiece which is being processed.